In recent years, avionics engineers have endeavored to provide pilots and flight crews with information necessary for safe flight. One approach has been to provide the flight crew with information on the location of other aircraft in the vicinity. The systems which provide this information, known as TCAS, are required for all airliners flying in United States air space. TCAS devices interrogate transponders of other aircraft, sometimes referred to as "intruder" aircraft. The TCAS then evaluates the threat of collision with the other aircraft and coordinates an escape for the aircraft.
Existing TCAS display devices provide the flight crew with a top view representation or format which graphically displays the distance and bearing of the intruder aircraft. Intruder altitude information, relative to a reference altitude, is provided numerically. Thus, the pilot must form his or her own mental picture of the relative altitude differences between the altitude of his or her aircraft and the current altitude of the intruder aircraft. Because this single view TCAS display format requires that the pilot interpret the display both graphically and numerically at the same time, the pilot's situational awareness is not optimal. This fact increases the chance that pilot error will cause a mid-air collision. Further, with the pilot's situational awareness reduced, other pilot errors can occur.